Hf» ROCKS OF THE TR A P P-FOR M ATlOtf, 



unnity, the heat is pointed out as refiding in the vein ; am! 

 this is to be accounted for only on the fuppofition of the 

 melted whin, at a period fubfequent to the confolidation of the 

 coal, having flowed through the openings of the ftrata. The 

 heat hi.s'been powerful enough in many places to drive off the 

 bituminous matter of the coal, and to force it into the colder 

 and more diftant parts. Few facts in the hiftory of foffils are 

 more remarkable than this, and none more directly affimilates 

 the operations of the mineral regions with thofe that take place 

 at the furface of the earth." 

 In reply. This An eminent Irifh geognoft is of opinion, that the appear* 

 effeft is afenbed ances defcribed by ProfefFor Playfair may have been produced 



to the percola- ■ *• - * ,1^1 r 1 i r 1 



tion of water, by. the percolation of water along the fides oi the balalt vein. 



This explanation will be fatisfaclory to thofe who have wit- 

 nefled the effects produced by the weather on coal. This al- 

 tered coal, however, muft not be confounded with the glanz 

 and columnar coal, becaufe thefe differ from it in oryctognot 

 tical and geognoftical characters. 



The argument contained in fection 69, is refuted by what 

 Werner mentions in his admirable book on the formation of 

 veins. 

 P. That the Seftion 71. " Again, if it be true that the mattes of whin- 

 introduced be- ^one, thus interpofed among the ftrata, were introduced there 

 tween the ftrata, after the formation of the latter, we might expect to find, at 

 Ihe' fimflarityof Ieaft in man >* inftances, that the beds on which the whinftone 

 the parts fo fepa- refts, and thofe by which it is covered, are exactly alike. If 

 thefe beds were once contiguous, and have been only heaved 

 up and feparated by the irruption of a fluid mafs of fubterranean 

 lava, their identity (hould frill be recognifed. Now this is 

 precifely what is obferved ; it is known to hold in avail num- 

 ber of inftances, and it is ftrikingly exemplified in the rock of 

 This argument Salifbury Crag near Edinburgh.-" If this argument was cor- 

 ^much,°be°- Verea ' lt mould foIIow > that the beds of foliated limeftone con- 

 caufe it would taining fhells, which are found between ftrata of fan d ft one, 



SddkftJataT had been e J eaed from below ' ThIs fea cannot be evaded 

 by faying, that the limeftone has been only foftened ; it is plain 



if the foliated fracture (according to the Huttonian fyftem) is a 



character of fufion in one ftone, fo muft it in all others. 



P. The nodales At fection 73 we have the following obfervations on the for- 



ftone^pp"^^" mation of agates : « Some of the fpecies of whinftone are the 



hayc been fluid j common matrices of agates and chalcedonies, which lie inclofed 



2 i» 



